Wrap-around type spectacle lenses are widely used, for example, in the field of sport. The wrap-around type spectacle lenses are configured to have a wide width and to be curved along the face so that the spectacle lenses cover the face. By wearing such spectacle lenses having a large face form angle of a frame, the wearer is able to have advantageous effects, such as, expansion of the field of view, windbreak and control of laterally entering light. The wearer wears wrap-around type spectacle lenses with dioptric power or wrap-around type spectacle lenses without dioptric power depending on presence or absence of visual acuity correction.
As pointed out, for example, in US Patent Application Publication No. 2012/8089 (hereafter, referred to as “patent document 1”), regarding wrap-around type spectacle lenses of this type, the prismatic effect, astigmatism and the average dioptric power error which the wearer feels are different from usually used ordinary spectacle lenses formed by fitting a lens into a frame having a small face form angle. Therefore, there is a case where a wearer who is wearing wrap-around type spectacle lenses has uncomfortable feeling. The patent document 1 pays attention to the fact that conventional design does not consider reducing unbalance between left and right prismatic effects, and considers that the unbalance is the cause of uncomfortable feeling which the wearer receives. The patent document 1 proposes a method where, in order to reduce unbalance between the left and right prismatic effects, shape data of a lens rear surface (a concave surface) is corrected such that prismatic effects given, by an initial lens having a lens front angle, to a plurality of light rays including a frontward viewing direction and passing through a rotation enter of an eye assumed in optical design coincide with or approach prismatic effects given, by an initial lens not having a lens front angle, to the plurality of light rays. It should be noted that the lens front angle is an angle formed, in a horizontal direction, by a visual line defined to pass the rotation center of the eye when a person without spectacle lenses views a far point and a normal line to a lens front surface (a convex surface) at a fitting point.